[Kotlin] fix 20228 - spring-kotlin insert override modifier to interface if it is needed (#20246)

modules/openapi-generator/src/main/resources/kotlin-spring/interfaceOptVar.mustache

@@ -2,4 +2,4 @@
         @get:Schema({{#example}}example = "{{{.}}}", {{/example}}{{#required}}requiredMode = Schema.RequiredMode.REQUIRED, {{/required}}{{#isReadOnly}}readOnly = {{{isReadOnly}}}, {{/isReadOnly}}description = "{{{description}}}"){{/swagger2AnnotationLibrary}}{{#swagger1AnnotationLibrary}}
         @get:ApiModelProperty({{#example}}example = "{{{.}}}", {{/example}}{{#required}}required = {{required}}, {{/required}}{{#isReadOnly}}readOnly = {{{isReadOnly}}}, {{/isReadOnly}}value = "{{{description}}}"){{/swagger1AnnotationLibrary}}{{#vendorExtensions.x-field-extra-annotation}}
         {{{.}}}{{/vendorExtensions.x-field-extra-annotation}}
-        {{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}? {{^discriminator}}= {{{defaultValue}}}{{^defaultValue}}null{{/defaultValue}}{{/discriminator}}
+        {{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}? {{^discriminator}}= {{{defaultValue}}}{{^defaultValue}}null{{/defaultValue}}{{/discriminator}}

modules/openapi-generator/src/main/resources/kotlin-spring/interfaceReqVar.mustache

@@ -2,4 +2,4 @@
         @get:Schema({{#example}}example = "{{{.}}}", {{/example}}{{#required}}requiredMode = Schema.RequiredMode.REQUIRED, {{/required}}{{#isReadOnly}}readOnly = {{{isReadOnly}}}, {{/isReadOnly}}description = "{{{description}}}"){{/swagger2AnnotationLibrary}}{{#swagger1AnnotationLibrary}}
         @get:ApiModelProperty({{#example}}example = "{{{.}}}", {{/example}}{{#required}}required = {{required}}, {{/required}}{{#isReadOnly}}readOnly = {{{isReadOnly}}}, {{/isReadOnly}}value = "{{{description}}}"){{/swagger1AnnotationLibrary}}{{#vendorExtensions.x-field-extra-annotation}}
         {{{.}}}{{/vendorExtensions.x-field-extra-annotation}}
-        {{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}
+        {{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java

@@ -851,6 +851,36 @@ public class KotlinSpringServerCodegenTest {
 
     }
 
+    @Test
+    public void overridePropertyFunction() throws IOException {
+
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+
+        KotlinSpringServerCodegen codegen = new KotlinSpringServerCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(CodegenConstants.SERIALIZABLE_MODEL, true);
+
+        ClientOptInput input = new ClientOptInput()
+                .openAPI(TestUtils.parseSpec("src/test/resources/bugs/issue_20228.yaml"))
+                .config(codegen);
+        DefaultGenerator generator = new DefaultGenerator();
+
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.SUPPORTING_FILES, "false");
+
+        generator.opts(input).generate();
+
+        assertFileContains(
+                Paths.get(outputPath + "/src/main/kotlin/org/openapitools/model/Pony.kt"),
+                "override val nameOpt", "override val nameReq"
+        );
+    }
+
     @Test
     public void generateSerializableModel() throws Exception {
         File output = Files.createTempDirectory("test").toFile().getCanonicalFile();

modules/openapi-generator/src/test/resources/bugs/issue_20228.yaml

@@ -0,0 +1,42 @@
+openapi: 3.0.3
+paths:
+  /api/kotlin-test:
+    post:
+      description: Example get
+      responses:
+        '200':
+          description: The request sent by the client was successful.
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Unicorn'
+components:
+  schemas:
+    Animal:
+      type: "object"
+      properties:
+        nameOpt:
+          type: "string"
+        nameReq:
+          type: "string"
+      discriminator:
+        propertyName: animalType
+        mapping:
+          pegasi: "#/components/schemas/Pony"
+    Pony:
+      allOf:
+        - $ref: "#/components/schemas/Animal"
+        - type: "object"
+      discriminator:
+        propertyName: ponyType
+        mapping:
+          pegasi: "#/components/schemas/Pegasi"
+          unicorn: "#/components/schemas/Unicorn"
+    Pegasi:
+      allOf:
+        - $ref: "#/components/schemas/Pony"
+        - type: "object"
+    Unicorn:
+      allOf:
+        - $ref: "#/components/schemas/Pony"
+        - type: "object"